Bristol-Myers Squibb (NYSE: BMY) CEO Lamberto Andreotti might call it a difference in opinion about how to proceed, but it's looking a lot more like a difference in pipelines.

Andreotti reportedly told investors at a conference yesterday that Bristol was still interested in continuing the development of its hepatitis C drug, daclatasvir, in combination with Gilead Sciences (Nasdaq: GILD) GS-7977, but that Gilead isn't willing to play ball.

The combination produced beautifully in a phase 2 trial with early cure rates between 91% and 100%, depending on the strain of virus. Some of those patients might relapse, but considering the combination doesn't require Merck's (NYSE: MRK) PegIntron or Roche's Pegasys, which have to be injected and carry unpleasant side effects, it's still outstanding data.

Why doesn't Gilead want to continue, then? The biotech has a drug, GS-5885, which is in the same class -- NS5A inhibitor -- as daclatasvir. Given the similarities, Gilead hopes to jump straight into phase 3 trials, testing GS-7977 with GS-5885. (Wonder if they'll call it GS-13862.) Assuming the in-house combo works, Gilead will get to keep all the revenue from the treatment rather than having to share it.

Bristol has a drug, INX-189, which it now calls BMS-986094, in the same class as GS-7977, from the acquisition of Inhibitex. I haven't seen any data combining the two, but Bristol's public announcement of its desire to partner with Gilead makes you think that there might be something wrong with BMS-986094. Of course, Johnson & Johnson (NYSE: JNJ) agreed to test its hepatitis C drug TMC435 with BMS-986094, so there's at least one company that thinks it's a viable drug.

At this point it looks like Gilead has the upper hand in negotiations, especially as Bristol hasn't been playing its cards very close to its vest. If Bristol really wants to develop a combination of GS-7977 and daclatasvir, it'll probably have to give up some of the economics on the combination drug. If BMS-986094 turns out to be a $2.5 billion blunder, accepting only 30% to 40% of a joint venture wouldn't be the end of the world.

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